netdev - Re: kernel stack trace using conntrack

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Message-ID: <4B7DF4DC.4000502@netfilter.org>
Date:	Fri, 19 Feb 2010 03:18:04 +0100
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Patrick McHardy <kaber@...sh.net>
CC:	Ramblewski David <David.Ramblewski@...sorigin.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: kernel stack  trace using conntrack

Patrick McHardy wrote:
> Pablo Neira Ayuso wrote:
>> Patrick McHardy wrote:
>>>>> Pablo, please let me know whether you want me to apply this.
>>>> ctnetlink_change_helper() also calls nf_ct_ext_add() for conntracks that
>>>> are confirmed (in case of a helper update for an existing conntrack).
>>>> That would also trigger the assertion. If we want to support helper
>>>> assignation via ctnetlink for existing conntracks, we will need to add
>>>> locking to the conntrack extension infrastructure to avoid races.
>>>>
>>>> I don't see a clear solution for this yet.
>>> I see, this is indeed a problem. Since the helper is known at the
>>> first event, we could restrict this to only allow manual assignment
>>> for newly created conntracks. Most helpers probably can't properly
>>> cope with connections not seen from the beginning anyways.
>> Indeed, changing the helper in the middle of the road doesn't make too
>> much sense to me either. I can send you a patch for this along today,
>> I'll find some spare time to do it.
> 
> Great, thanks Pablo.

I have slightly tested the following patch here. I think it should fix
the problem.

We can revisit ctnetlink_change_helper() later, I think there's some
code there that can be refactorized.

Let me know if you're OK with it.

View attachment "fix-helper.patch" of type "text/x-patch" (2842 bytes)